The current study investigated whether contextual effect could be found in object-based attention when task-related features are part of the object using the Egly, Driver, and Rafal (1994)'s cueing paradigm. There were two possible accounts that differently predicted the processing of attended objects. Firstly, attentional spreading account argues object-based attention arises from the enhancement of the representation of an attended object as compared to an unattended object. In contrast, attentional prioritization account asserts the attentional priority in which an attended object is searched earlier than an unattended object. According to a previous research which supports attentional spreading account, a target integral to the object, such as concave stimulus, is known to induce attentional spreading through the object boundaries. We varied the probability of target occurrences in potential locations of the target and measured on the effect of the object-based attention using a concave stimulus. In Experiment 1, participants were instructed to determine whether the target concave was rectangular or circular. The target appeared in the cued location on half the trials. On half of invalidly cued trials, the target appeared either in the high-probability location or in the low-probability location. We found statistically significant effect of object and contextual effect. However, there was no significant interaction between the two effects. In Experiments 2 and 3, participants detected only the presence of the target. The target was present in the cued location on half the trials in Experiment 2 and on 70% of the trials in Experiment 3. The result of both of the experiments also showed a significant object and context effect but not a significant interaction between object and context effect. These results indicate that object and contextual effect of visual attention would depend on the kind of task as well as the sort of stimulus.